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Malignant Bone Tumours


Chondroid Origin

Chondrosarcoma

Definition

  • A malignant cartilage-producing tumour – it generally has a better prognosis than an osteosarcoma (due to late metastases)

  • Classification:

    • ▪

      Central (intramedullary) vs peripheral

    • ▪

      Primary vs secondary (e.g. arising in a pre-existing bone lesion such as a central enchondroma or a peripheral osteochondroma)

    • ▪

      Grade I: low grade ▸ Grade II: myxoid ▸ Grade III: high grade ▸ dedifferentiated: this refers to the development of an adjacent non-chondroid tumour (e.g. an osteosarcoma, fibrosarcoma, or MFH)

  • A major consideration is the differentiation between a chondroma and a low-grade chondrosarcoma

Clinical Presentation

  • This is rare in children with > 50% of patients over 40 years of age (M : F, 1.5 : 1) ▸ secondary chondrosarcoma tends to present at a slightly younger age (4th + 5th decades)

  • Most are low-grade tumours found incidentally ▸ it can present with insidious pain, a palpable mass or a pathological fracture

Location

It usually affects the pelvis, proximal femur and proximal humerus (it is rare distal to the elbow or knee) ▸ it is found within the metaphysis (± epiphyseal extension) ▸ 9% of chondrosarcomas occur in the ribs, making this the most common rib primary (other than myeloma) ▸ rare in the hands and feet (c/w enchondroma)

Radiological Features

  • General features of central chondrosarcoma are those of a lytic lesion, well-defined in low grade cases and progressively ill-defined in higher grade cases

XR

A well-defined lytic lesion with chondroid matrix mineralization (chondroid calcification visible in 75%, described as ring-and-arc, punctate, stippled or popcorn) ▸ there is a narrow zone of transition

  • Slow growth: this allows reactive change with periosteal new bone + bone expansion + endosteal resorption (endosteal scalloping > of the cortical width suggests a chondrosarcoma rather than a chondroma) ▸ an increased cortical thickness (if the periosteal reaction outweighs the cortical scalloping)

  • More aggressive tumours: cortical destruction ▸ one should consider dedifferentiation to a more malignant type

CT/MRI

This can demonstrate a large extraosseous mass which is commonly seen with pelvic lesions (which are often radiographically and clinically occult)

  • T1WI: hypointense to muscle ▸ T2WI: multilobulated high SI lesion ▸ matrix mineralization appears as foci of signal void ▸ T1WI + Gad: minimal peripheral or septal enhancement (as it is poorly vascularized)

Scintigraphy

A chondrosarcoma will demonstrate greater activity than that seen within the anterior iliac crest ▸ cannot reliably distinguish between benign and malignant lesions

Pearls

  • Suspect the development of a chondrosarcoma within a pre-existing osteochondroma if:

    • ▪

      There is increased pain or continued growth after skeletal maturity

    • ▪

      There is destruction of part of the calcified cap or ossified stem

    • ▪

      US/CT/MRI: these can assess the cartilage cap – it should be < 5 mm with an osteochondroma (but is often > 20 mm with malignant change)

Periosteal chondrosarcoma (juxtacortical chondrosarcoma)

  • This is rare (and more common in men) ▸ it involves the outer long bones (usually the distal femoral or proximal humeral metaphyses) ▸ there is a good prognosis after resection

XR

A calcificed juxtacortical cartilagenous mass (>5 cm in length) with cortical thickening and periosteal reaction ▸ distinguished from the other surface form of chondrosarcoma (peripheral chondrosarcoma) by a lack of continuity with underlying medullary bone

Mesenchymal chondrosarcoma

  • This is rare, affecting a younger age group than with a conventional chondrosarcoma (3 rd and 4 th decades) ▸ it has a very much more cellular malignant matrix than a normal chondrosarcoma (high grade malignancy)

XR

It is indistinguishable from a central chondrosarcoma ▸ there is often chondroid calcification ▸ there is a predilection for the ribs and mandible

  • Local recurrence and metastases occur early (and more commonly than with a conventional chondrosarcoma)

Clear cell chondrosarcoma

  • This is rare ▸ it is a low-grade tumour with a better prognosis and slow growth ▸ can be mistaken for a subchondral cyst/intraosseous ganglion

XR

It resembles a chondroblastoma or chondromyxoid fibroma – except it almost always involves the ends of the long bones after closure of the growth plate (esp. the proximal femur or humerus) ▸ it has a lytic appearance (± a loculated or ‘soap bubble’ appearance)

Chondrosarcoma. AP XR showing a mineralized lesion of the fibula due to low-grade chondrosarcoma. The lesion cannot be radiologically differentiated from a chondroma. *

AP radiograph of the femur showing an extensive central chondrosarcoma with typical chondroid matrix, cortical expansion and thickening with endosteal scalloping. **

Dedifferentiated chondrosarcoma. AP XR showing a proximal femoral chondrosarcoma with an adjacent area of lytic destruction and a pathological fracture. *

AP radiograph of the hip showing a clear-cell chondrosarcoma as a well-defined lytic lesion extending up to the articular margin. **

Chondrosarcoma of the left ilium. Axial CT (A) and T2WI (B) show a large extraosseous mass. *

Peripheral chondrosarcoma. (A) AP XR showing an osteochondroma of the distal fibula (arrows). (B) Axial fat-suppressed T2WI shows a large malignant cartilage cap surrounding the osteochondroma (arrow) and causing pressure erosion of the adjacent tibia (arrowheads). *

Chondrosarcoma of the femur. (A) Coronal T1WI and (B) STIR image show a large lobulated intramedullary lesion, which is particularly hyperintense on STIR. *

Osteosarcoma

Conventional central osteosarcoma

Definition

  • Commonest non-haematological primary bone malignancy ▸ a malignant osteoid producing tumour

  • It is usually a primary central osteosarcoma (75%) – the remainder are made up of other variants distinguished by site and histological grade ▸ it can occur secondary to Paget's disease, post radiotherapy or as a dedifferentiated chondrosarcoma

  • Classification:

    • ▪

      Central (conventional high or low grade)

    • ▪

      Intracortical

    • ▪

      Surface (parosteal, periosteal or high grade)

Clinical Presentation

  • Pain or a palpable mass (usually > 6cm at presentation) ▸ pathological fracture

  • 80% of cases present between 10 – 30 years ▸ uncommon under 10 years of age ▸ rare under 5 years of age ▸ there is a 2 nd smaller peak occurring above the age of 40 years which is seen commonly within the flat bones and vertebrae and usually secondary to a pre-existing disorder (e.g. Paget's)

Radiological Features

Location

it commonly affects the metaphyseal region of a growing long bone (50-75% are seen around the knee, and within the distal femur or proximal tibia) ▸ other common sites include the proximal humerus and femur ▸ it can cross the growth plate with epiphyseal extension seen in 75% of cases

XR

moth-eaten or permeative lytic bone destruction arising eccentrically within the medullary cavity – there can be associated medullary sclerosis due to mineralised tumour osteoid (which has been described as ‘solid’, ‘amorphous’, ‘cloud-like’ and ‘ivory-like’) ▸ there is a wide zone of transition ▸ there can be cortical destruction with an extra-osseous mass and cloudlike matrix mineralization ▸ a spectrum of appearances from purely lytic (13%) to purely sclerotic

  • Periosteal reaction: a ‘sunburst' appearance perpendicular to the cortex ▸ a lamellated / onion skin appearance with reactive Codman's triangles seen at the margins of the lesion

  • A solely lytic lesion (13% of cases) may mimic an ABC

MRI

this adds little to the diagnosis but is invaluable for local staging and assessing any extension (it can demonstrate any intramedullary and extraosseous extension as well as extension into the adjacent joint or across an open growth plate)

FDG PET

established role in the evaluation of treatment response and for recurrent disease

Pearls

  • It is a highly vascular tumour with early haematogenous metastases to the lung (with a subpleural location, possible calcification, and potential pneumothorax formation) ▸ occasionally there are lymphatic metastases

    • ▪

      ‘Skip metastases’: metastasis within the same bone as the primary (5-8% of cases)

    Lytic osteosarcoma. Lateral XR of the distal femur showing a lytic osteosarcoma. *

    Low-grade central osteosarcoma. AP XR of the proximal humerus showing the lytic, trabeculated pattern. *

    Pseudocystic osteosarcoma. AP XR of the proximal fibula showing an expanded, lytic lesion mimicking an aneurysmal bone cyst. *

    Conventional central osteosarcoma. (A) AP XR of the distal femur showing a classical osteosarcoma with mixed lytic and sclerotic areas, tumour bone formation in the extraosseous mass (arrow), and a proximal Codman's triangle (arrowhead). (B) AP XR of the proximal tibia showing dense metaphyseal sclerosis due to an osteoblastic osteosarcoma. *

    Radiation-induced sarcoma of the left superior pubic ramus manifest as a region of lytic bone destruction (arrow) with underlying radiation osteitis. *

    Paget's sarcoma. (A) AP XR of the proximal femur showing Paget's disease. (B) Axial T1WI shows an associated large soft tissue mass due to sarcomatous change. *

Other Varieties of Osteosarcoma

Other Varieties of Central Osteosarcoma

Primary multicentric osteosarcoma

  • Multiple intramedullary osteosarcomas in the absence of pulmonary metastases

  • Synchronous: multiple osteoblastic metaphyseal lesions occurring in children or adolescents ▸ it has a poor prognosis

  • Metachronous: this affects older patients presenting with a solitary lytic or sclerotic lesion within a long or flat bone ▸ multiple lesions are seen after more than 5 months ▸ this has a better prognosis than a synchronous lesion

Telangiectatic osteosarcoma

  • This is composed of septated blood-filled cavities (and can mimic an ABC) ▸ it accounts for 4-11% of all osteosarcomas with a mean age of presentation at 24 years (M:F 2:1) ▸ it is very malignant with a poor prognosis

Location

femur, tibia and humerus

XR

predominantly lytic lesions ± bone expansion

CT / MRI

subtle matrix mineralisation ▸ extensive haemorrhage with fluid-fluid levels ▸ extra-osseous extension

  • Thick peripheral, septal and nodular enhancement helps differentiate from an ABC

Small cell osteosarcoma

  • This accounts for <1% of cases ▸ it has similar features to a conventional central osteosarcoma

Low-grade intramedullary osteosarcoma

  • This well differentiated indolent lesion accounts for <1% of cases ▸ there is a mean age of presentation at 34 years, with a slight female preponderance

Location

the femur and tibia (around the knee)

XR / CT

4 patterns: 1) lytic with varying degrees of coarse trabeculation ▸ 2) lytic with little trabeculation ▸ 3) densely sclerotic ▸ 4) mixed lytic and sclerotic

  • It has a relatively benign appearance that can be mistaken for fibrous dysplasia, osteoblastoma or a low grade chondroid tumour ▸ extraosseous extension aids in the differentiation

Surface Osteosarcoma

Definition

A group of tumours that arise form the surface of bone – includes parosteal, periosteal and high grade surface osteosarcomas ▸ all types account for < 10% of osteosarcomas

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